1. Field of the Invention
The invention relates to a multi-source CT system for the generation of X-ray images of an object under examination of the type having at least one first and one second X-ray radiation source mounted in a rotatable manner about a rotational axis, each emitting a radiation beam and at least one X-ray radiation detector that is struck by the radiation beams.
2. Description of the Prior Art
A significant future requirement of computer tomography (CT) scanners is ever greater rotational frequencies of gantries. A faster rotation of the gantry around the patient shortens the recording (data acquisition) time, which in turn results in higher temporal resolution of the recordings. This is of great importance in cardiology in particular, as here a high temporal resolution at the beating heart also influences spatial resolution and thus the possibility of detecting arteriosclerosis at an early stage. In the case of higher rotational frequencies, however, the mAs requirement must also be met in order to reach a certain image quality. Ever greater radiation power must be delivered, so that these X-ray tubes must be specially designed for the requisite short-term load of typically 1 s.
An increase in the rotational frequency, however, also increases the strain on the components of the gantry as a result of greater centrifugal force, so that the rotational frequency is currently limited to 3 to 4 Hz. In order nonetheless to increase the number of projections achieved per unit of time, the use of dual- or multi-tube CT systems is known, in which two or more X-ray emitter-detector units are arranged, offset at an angle in a gantry housing. Furthermore, a known method for better differentiation of a variety of tissue types is to scan the area under investigation simultaneously with X-ray radiation of different spectral distribution, that is to say with different maximum X-ray energy or a different spectral centroid.
A dual-source CT system for examination of a patient is known from DE 10 2007 024 158 A1, having a gantry housing, in which two X-ray tubes are arranged offset an at angle with oppositely arranged detector systems, which rotate about a system axis for scanning of the patient, while the patient is conveyed along the system axis through the measuring area of the CT system by means of the controllable patient couch. During a dual-energy CT examination, the two similar X-ray tubes are operated with different acceleration voltages, so that the two X-ray spectra used differ greatly and also deliver different absorption values in the assigned detectors upon irradiation of the patient.
In addition to short-duration scans with a maximum of a few seconds duration, CT systems are also used for whole-body scans and perfusion measurements. In such cases the X-ray emitter must be designed for recording times of up to one minute. The X-ray emitter that has been designed so as to be able to be used in short-term scans is subjected to extreme stresses in such longer term operation, which in particular impacts its useful life.